ADDED: Number db query

Added the number db query, this can be used when the rest of the contact's information (Such as other numbers, or their name or the messages from that contact) are not needed. Rather then getting the entire TrustedContact object from the db a query and then accessing only a single Number stored.
Merge branch 'master' of github.com:tinfoilhat/tinfoil-sms
REFACTOR: getRow that just needed getNumber

In most cases getRow() was used to get access to the Number and not the entire contact. Use of getNumber() was employed since it will be more effective and less costly.
MODIFIED: database new table exchange_messages

The new table will help support non-automatic key exchange management.